1. Field of the Invention
This invention relates to a semiconductor device.
2. Description of the Related Art
Conventional semiconductor devices have been described in, for example, Japanese Patent Laid-open Nos. 2002-231815 and 2004-39951. In the semiconductor device described in these references, in an interconnection layer, a dummy interconnection is formed together with a common interconnection. A dummy interconnection is formed for a local uniform data rate in an interconnection layer. Here, a data rate refers to an area rate of an interconnection in an interconnection layer. A uniform data rate can improve uniformity in a thickness of a Cu buried in forming an interconnection, and also provide a Cu interconnection with higher flatness in subsequent CMP (Chemical Mechanical Polishing).
Some semiconductor devices having a multilayer interconnection structure has a dummy interconnection in each interconnection layer. For such a semiconductor device, it has been technically common to commonly use, among all interconnection layers, a dummy interconnection having a width in accordance with an interconnection rule for a global interconnection, in order to reduce a data volume of EB data (Electron Beam Exposure Data) for drawing a mask. In other words, increase of EB data volume has been reduced by using dummy interconnections with an equal size in all interconnection layers, whose width are relatively larger.
However, there is room for improvement in a conventional semiconductor derive with the above configuration in terms of an yield. After intense investigation, we have found out the causes for yield reduction in a conventional semiconductor device. Specifically, although a local interconnection has a smaller width and a smaller thickness than a global interconnection, a dummy interconnection with a size in accordance with an interconnection rule for a global interconnection is disposed near a local interconnection in a conventional semiconductor device.
Thus, in a process for manufacturing the semiconductor device, during etching a groove for a local interconnection, there may be unevenness in a width and a thickness of a groove between an area near a dummy interconnection and an area not near a dummy interconnection. There is a big difference of etching rate between an area near a dummy interconnection and an area not near a dummy interconnection. It is because in an area near a dummy interconnection, a larger amount of etchant is consumed for a groove for the dummy interconnection.
Recently, as a thickness of a local interconnection has become thinner, influence of the above-described unevenness has become significant, and thus it has been probably manifested as reduction in an yield of a semiconductor device.